The present invention relates to a method and a device for temporarily setting up one or several sondes against the inner wall of a cased well. The well sonde according to the invention can be installed in a well for example for various operations connected with the production of hydrocarbons.
A well equipped for petroleum production for example comprises a casing set up during the drilling operations. It is held in position with cement injected into the annular space between the casing and the wellbore. A tubing for the flowing of the fluids outside the producing zone is set up in the cased well.
The well sonde according to the invention can be used in this case for containing seismic or acoustic sensors (accelerometers, geophones, piezoelectric sensors, etc) which are to be coupled with the casing for the passive monitoring of the zone in production to determine the evolution thereof in time for example.
The well sonde according to the invention can also be used for example within the framework of operations for the hydraulic fracturing of a petroliferous zone where a fluid under pressure is injected into a confined well portion to generate fractures therein, in order to favour the production thereof. It is well-known that, in this type of operations, it is useful to set up in the well a sonde fitted with directional sensors sensitive to the noises transmitted by the rocks subjected to the fracturing fluid, in order to determine the directions of propagation of the fractures. Temperature and pressure sensors can also be included in such a sonde.
Various sondes which can be used within the framework of hydraulic fracturing operations are well-known through U.S. Pat. No. 4,690,214 4;898,237 4,898,240 and 4,898,241 assigned to the same assignee. They are taken down as far as the intervention zone by means of a tubing constituted by interconnecting tubular sections and linked to a surface control and recording installation by an electric carrying cable which can possibly be connected when the sonde has already been taken down into the well. Using such a tubing sometimes presents drawbacks for some applications. It is the case for fracturing operations where propping agents must be injected through the tubing, which, as can be noticed, tend to erode the electric carrying cable and sometimes to obstruct the tubing, which sometimes prevents from taking up the sonde after using it.
A process and a device for installing a reception array in a well, which essentially consists in arranging sensors outside the casing and in drowning them in the cement injected into the annular space between the casing and the well, are well-known through U.S. Pat. No. 4,775,009. This process provides a particularly good coupling of the sensors with the surrounding formations. It is suitable for a stationary installation because of the irreversible nature thereof.